In this lesson, we’re going to discuss the general trends in the periodic table. This is a crucial part of chemistry, and it’s the last lesson we’ll cover in this subject (The Periodic Table).

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Density

Firstly, let’s talk about density. Density is defined as mass divided by volume, represented by the formula . As we move down a group in the periodic table, the mass of the elements increases. This means that the density also increases down the group.

Hardness

Next, we’ll discuss hardness. For non-metals, hardness increases as we go down the group. This trend is evident when studying the chemistry of halogens. As we move down the group, we transition from gases to solids, indicating an increase in hardness. However, for metals, such as alkali metals and alkali earth metals, the hardness decreases down the group.

Fixed Points

Fixed points behave similarly to hardness. For non-metals, fixed points increase down the group, while for metals, they decrease. The harder the substance, the more energy is required to overcome the forces of attraction, resulting in higher fixed points.

Metallic and Non-metallic Character

The metallic character increases down the group, while the non-metallic character decreases. This trend is directly related to reactivity. The more metallic or non-metallic an element is, the more reactive it is. Therefore, reactivity increases down the group for metals and decreases for non-metals.

State Changes

As we move down a group, the state of the elements changes from a gaseous form to a solid form.

Now, let’s discuss the trends across the period.

State Changes Across the Period

As we move across the period, the state changes from a solid form to a gaseous form. This is because we move from heavy metals on the left to heavy non-metals on the right.

Metallic Character Across the Period

The metallic character decreases across the period, while the non-metallic character increases.

Hardness and Fixed Points Across the Period

Hardness and fixed points increase up to the middle of the periodic table (where we find carbon in the form of diamond, the hardest known substance), and then they decrease.

Reactivity Across the Period

For metals, reactivity decreases across the period, while for non-metals, it increases.

In summary, we’ve discussed the general trends in the periodic table, both down the groups and across the periods. We’ve covered density, hardness, fixed points, metallic and non-metallic character, reactivity, and state changes. Understanding these trends will help you predict the properties of elements and their reactions.